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I'm planning on having a Unico or Spacepak system installed in our 1968 split level home which currently has hydronic heating. We've had both Uncio and Spacepak contractors quote on the job, but we've gotten different answers from all vendors, who is correct?

Our home is around 3900sq ft. with two levels being above grade, one level partially below grade and the lowest level completely below grade. We live in Michigan, so the summers are not super hot, but we did have many days in the 90's this year. As the two lower levels maintain a lower temperature then the upper two it has been suggested by all contractors that we install a system only on the upper two levels which comprise about 2000-2500sq ft and as cool air descends it will naturally keep the lower levels cool. The home has blown cellulose insulation, 10 ft. ceilings on the upper level, and 15ft ceilings on the living room, dining room and kitchen level. We have large glass exposure on the living room level, but this faces North. Other then this we have typical glass exposure on the South side bedroom levels. We have shade tree coverage on 50% of the roof area by mid spring.

The problems begin when they start recommending systems. Two contractors are suggesting we use a 5 ton condenser with a larger Unico system air handler with around 30 to 31 diffusers. Two others are suggesting we use a 3 1/2 ton compressor with a smaller Unico air handler and around 20 to 21 diffusers. The final one is recommending a 3 1/2 ton unit with only 17 diffusers, and insists that Unico recommends no more then 5 diffusers per ton. However upon calling Unico direct I was told they recommend no less then 6 diffusers per ton, so obviously the latter contractor is no longer being considered.

We prefer it to be a little cooler then most, so we wouldn't mind the extra headroom a 5 ton might provide, but understand that if the condenser is oversized that the unit might not remove as much humidity on cooler days when the system wouldn't be on as much. Would it make any sense to go to a 4 Ton and split the difference? I called Unico direct and talked to a rep, but he said they all could be right (not the answer I was looking for). Not being a HVAC professional, just a confused consumer, I'm lost as to which company is right and which is wrong, any HVAC professionals with an opinion on who is right and who is wrong?

Also one vendor carries and suggested the Spacepak system. From the outside they look the same to me. I have read that Spacepak was the first, and that Unico started from some employee's that left Spacepak when it was sold to another company. Is there anyone who has installed both who has an opinion on durability and quality of Spacepak versus Unico? or consumers who have had either system with good or bad experiences?

Did either one of your contractor's do a load calculation on the home? Sounds like they are just guess work by square ft.Unico told us to use 8 drops per ton of a/c and I have done about 6 systems in the past 3 years..

Only one did

The one who is offering Spacepak did a computer based load calculation a couple of years ago when we were first considering this, but didn't go ahead with it at the time.

He had a Unico rep come in with him and input all the info. However he now is a Spacepak dealer, and it seems to me that he's just reusing the Unico data for the Spacepak quote as he only spent about 15min. in our home when we asked him for the re-quote. Are these systems so similar that the data for one is interchangable with the other?

I would not start overcooling rooms so more air will go to the lower level. I would stay with the smaller systems and add a mini-split to the lower level if needed at a later date. If you go 4 ton you will need 25 to 30 drops which sounds like alot for one floor!

I know it is 6 per ton minimum, but if you are having longer runs or 50% drops you must engineer the system correctly.

Look at the ARI ratings. Those HV units suck the capacity. While you may be getting a "5 ton" outdoor unit, ARI rated capacity could be considerably less and so will SEER. Not unusual to find a 5 ton outdoor unit give 4 tons of cooling. So compare the ratings to an accurate load calc.

He didn't provide us with the load estimate, just a system quote. I think he was worried other contractors might use the data for a quote against him.

The system will be on two floors, totaling around 2500sq. ft.

As for the amount of cooling we've been using. None. As the home has hydronic heating and no ductwork we have no way to cool it other then window units, but we have casement windows, so even that would be hard. Both my wife and I dislike window units so we've had to grin a bear it until we can afford to make this addition. My wife who is 6 months pregnant didn't enjoy this summer, so we're doing this now before the baby comes.

I cool my 2000 s.f Connecticut colonial with 2 tons, so please do not oversize. I would use the hvac-calc load estimating software sold on this site to be sure you need 3.5 tons. What you do not realize is how much $$$ gets waisted when a system is oversized. If you cycle the compressor all day you drive up your electric bill by 50%.

On a design temp day a properly sized HVAC system will not cycle off at all.